|Publication number||US7053400 B2|
|Application number||US 10/838,330|
|Publication date||May 30, 2006|
|Filing date||May 5, 2004|
|Priority date||May 5, 2004|
|Also published as||CN1950946A, CN100533766C, DE112005001029T5, US20050247926, US20060208250, WO2005112127A1|
|Publication number||10838330, 838330, US 7053400 B2, US 7053400B2, US-B2-7053400, US7053400 B2, US7053400B2|
|Inventors||Sey-Ping Sun, David E. Brown|
|Original Assignee||Advanced Micro Devices, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Non-Patent Citations (4), Referenced by (36), Classifications (22), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to micro-miniaturized semiconductor devices comprising transistors on silicon-germanium. The present invention is particularly applicable in fabricating transistors with enhanced channel carrier mobility.
The relentless pursuit of miniaturized high speed semiconductor devices continues to challenge the limitations of conventional semiconductor materials and fabrication techniques. Conventional semiconductor devices typically comprise a plurality of active devices in or on a common semiconductor substrate, e.g., CMOS devices comprising at least a pair of PMOS and NMOS transistors in spaced adjacency. Current technology utilizes crystalline semiconductor wafers as substrates, such as a lightly p-doped epitaxial (“epi”) layer of silicon (Si) grown on a heavily-doped, crystalline Si Substrate. The low resistance of the heavily-doped substrate is necessary for minimizing susceptibility to latch-up, whereas the light doping of the epi layer permits independent tailoring of the doping profiles of both the p-type and n-type wells formed therein as part of the fabrication sequence, thereby resulting in optimal PMOS and NMOS transistor performance.
The use of the very thin epi layers, i.e., several μm thick, is made possible by utilizing shallow trench isolation (“STI”), which advantageously minimizes up-diffusion of p-type dopant(s) from the more heavily-doped substrate into the lightly-doped epi layer. In addition, STI allows for closer spacing of adjacent active areas by avoiding the “bird's beak” formed at the edge of each LOCOS isolation structure. STI also provides better isolation by creating a more abrupt structure, reduces the vertical step from active area to isolation to improve gate lithography control, eliminates the high temperature field oxidation step that can cause problems with large diameter, i.e., 8 inch, wafers, and is scalable to future logic technology generations.
Substrates based on “strained silicon” have attracted interest as a semiconductor material which provides increased speeds of electron and hole flow therethrough, thereby permitting fabrication of semiconductor devices with higher operating speeds, enhanced performance characteristics, and lower power consumption. A very thin, tensilely strained, crystalline silicon (Si) layer is grown on a relaxed, graded composition of silicon-germanium (Si—Ge) buffer layer several microns thick, which Si—Ge buffer layer in turn is formed on a suitable crystalline substrate, e.g., a Si wafer or a silicon-on-insulator (SOI) wafer. The Si—Ge buffer layer typically contains 12 to 25 at. % Ge. Strained Si technology is based upon the tendency of the Si atoms, when deposited on the Si—Ge buffer layer, to align with the greater lattice constant (spacing) of Si and Ge atoms therein (relative to pure Si). As a consequence of the Si atoms being deposited on a substrate (Si—Ge) comprised of atoms which are spaced further apart, they “stretch” to align with the underlying Si and Ge atoms, thereby “stretching” or tensilely straining the deposited Si layer. Electrons and holes in such strained Si layers have greater mobility than in conventional, relaxed Si layers with smaller inter-atom spacings, i.e., there is less resistance to electron and/or hole flow. For example, electron flow in strained Si may be up to about 70% faster compared to electron flow in conventional Si. Transistors and IC devices formed with such strained Si layers can exhibit operating speeds up to about 35% faster than those of equivalent devices formed with conventional Si, without necessity for reduction in transistor size. Conventional practices based on strained silicon technology also involve epitaxially growing a relaxed silicon layer on a tensilely stressed silicon layer which is subsequently doped to form relaxed source/drain regions in the relaxed silicon layer.
The mobility of electrons is faster than the mobility of holes in conventional bulk silicon substrates. Accordingly, in conventional CMOS transistors, the drive current of the PMOS transistor is less than the drive current of the NMOS transistor creating an imbalance. This imbalance is exacerbated in CMOS transistors fabricated on or within a tensilely stressed active device area formed in a strained lattice semiconductor substrate, e.g., strained Si on Si—Ge, because the increase in electron mobility is greater than the increase in hole mobility.
As micro-miniaturization proceeds, there is an attendant need to increase the drive current of transistors, including transistors formed on various types of strained Si—Ge substrates, by enhancing carrier mobility. Accordingly, there exists a need for methodology enabling the fabrication of semiconductor devices comprising transistors formed on Si—Ge substrates with enhanced drive currents by increasing channel carrier mobility and the resulting semiconductor devices.
An advantage of the present invention is a method of fabricating a semiconductor device comprising transistors on Si—Ge substrates with enhanced drive currents.
Another advantage of the present invention is a semiconductor device comprising transistors based on Si—Ge substrates with enhanced drive currents.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are obtained in part by a semiconductor device comprising: a substrate comprising a layer of silicon (Si) having a strained lattice on a layer of silicon-germanium (Si—Ge); a transistor comprising source/drain regions and a gate electrode over the substrate with a gate dielectric layer therebetween; and a stressed dielectric liner over side surfaces of the gate electrode and over the source/drain regions.
Another advantage of the present invention is a method of manufacturing a semiconductor device, the method comprising: forming a substrate comprising a layer of silicon (Si) having a strained lattice on a layer of silicon-germanium (Si—Ge); forming a transistor comprising source/drain regions and a gate electrode, having an upper surface and side surfaces, over the substrate with gate dielectric layer therebetween; and forming a stressed dielectric liner over the side surfaces of the gate electrode and over the source/drain regions.
Embodiments of the present invention comprise forming dielectric sidewall spacers on side surfaces of the gate electrode, such as an oxide liner and a nitride layer thereon, epitaxially growing a relaxed Si layer on the strained Si layer, forming source/drain regions in the relaxed Si layer and then depositing the stressed dielectric liner on the sidewall spacers, on the relaxed source/drain regions and on a portion of the strained Si layer between the sidewall spacers and raised source/drain regions.
Embodiments of the present invention also include forming dielectric sidewall spacers on side surfaces of the gate electrode, forming source/drain regions in the strained Si layer, forming a metal silicide layer on the upper surface of the gate electrode and a metal silicide layer on the source/drain regions, removing the dielectric sidewall spacers to expose a portion of the strained Si layer adjacent the side surfaces of the gate electrode, and then forming the stress dielectric liner on the metal silicide layer, on the upper surface of the gate electrode, on the side surfaces of the gate electrode, on the adjacent exposed portions of the strained Si layer, and on the silicide layer overlying the source/drain regions.
In embodiments of the present invention comprising N-channel transistors, the stressed dielectric liner exhibits high tensile stress. In embodiments of the present invention comprising P-channel transistors, the stressed dielectric liner exhibits high compressive stress. The stressed dielectric liner may comprise a layer of silicon nitride, silicon carbide or silicon oxynitride, at a thickness of about 200 Å to about 1000 Å.
Embodiments of the present invention include fabricating semiconductor devices comprising complimentary MOS (CMOS) transistors, with a compressive film on the PMOS transistor and a tensile film on the NMOS transistor. According to one aspect of this invention, process flow includes depositing a compressive stressed nitride film over both the NMOS and PMOS transistors, and then depositing a thin buffer film, such as an oxide or oxynitride film, over both the NMOS and PMOS transistors. Selective etching is then conducted to remove the oxide and compressive stressed nitride films from the NMOS transistor while masking the PMOS transistor. A tensile stressed nitride film is then deposited over both the NMOS and PMOS transistors, and then selectively etched away from the PMOS transistor. The resulting CMOS device comprises an NMOS transistor with a tensile stressed film thereon and a PMOS transistor with a compressive stress film thereon.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.
Transistors built on Si—Ge substrates involve different considerations than those built on bulk silicon substrates. Because of the large thickness of silicon substrates, stressed films deposited thereon tend to affect the substrate with a stress opposite to that exhibited by the film. For example, if a tensile stressed film is deposited on a bulk silicon substrate, compressive stress is imparted to the substrate and, hence, a channel region. However, typically, and in accordance with embodiments of the present invention, Si—Ge substrates are formed with a strained silicon layer having a thickness of about 200 Å to about 300Å. Relaxed source/drain regions may be formed thereon at a thickness of up to about 400 Å. Thus, the thickness of the strained Si layer and drain/source regions together typically does not exceed 800 Å. As a result, the strained Si layer, even together with a relaxed Si layer, is relatively transparent to the type of stress exhibited by a film deposited thereon. Accordingly, a tensile stressed layer deposited on a strained Si layer, or a relaxed Si layer formed on a strained Si layer, would also impart tensile stress to a channel region formed therein; and a compressive stressed layer deposited on such a thin Si layer or layers imparts compressive stress to a channel region formed therein; whereas, in bulk substrates, the opposite would occur.
The present invention addresses and solves the problem of increasing the drive current of transistors based on strained Si substrates in a cost effective and efficient manner by significantly enhancing the channel carrier mobility. The present invention stems from the recognition that the channel carrier mobility of transistors based on strained Si substrates can be increased by applying a stress thereto. In forming P-channel transistors, channel carrier mobility is enhanced by applying a stressed dielectric layer exhibiting high compressive stress for increasing hole mobility. In N-channel transistors, channel carrier mobility is significantly increased by applying a stressed layer exhibiting high tensile stress for increasing electron mobility. Stressed dielectric layers may be applied to transistors wherein the source/drain regions are formed within the strained Si layer, and to transistors having relaxed source/drain regions formed on strained Si layers. The stressed dielectric layer may comprise silicon carbide, silicon nitride or silicon oxynitride, and may be deposited by plasma enhanced chemical vapor deposition (PECVD) at a thickness of about 200 Å to about 1000 Å. Conventional PECVD conditions may be employed for deposition of a highly compressive or highly tensile dielectric layer. In depositing a stressed dielectric layer exhibiting high compressive stress, both high frequency and low frequency power are applied. When depositing a stressed dielectric layer exhibiting high tensile stress, the low frequency power is significantly reduced. In depositing a dielectric layer exhibiting high tensile stress, a tensile stress is applied to the underlying strained or relaxed Si layer. In applying a layer exhibiting high compressive stress, a compressive stress is applied to the underlying strained or relaxed Si layer.
For example, a stressed conformal silicon nitride layer exhibiting a high compressive stress, e.g., greater than 1 GPa, may be deposited at: a silane (SiH4) flow rate of 200 to 500 sccm; a nitrogen (N2) flow rate of 2,000 to 10,000 sccm; an ammonia (NH3) flow rate of 2,500 to 5,000 sccm; a SiH4/NH3 ratio of 0.2 to 0.04, a temperature of 350° C. to 550° C.; a pressure of 1 to 6 Torr; a high frequency power of 70 to 300 watts; a low frequency power of 20 to 60 watts and an electrode (shower head) spacing of 400 to 600 mils. A silicon nitride layer exhibiting a high tensile stress, e.g., greater than 1 GPa, may be deposited at a SiH4 flow rate of 50 to 500 sccm; an NH3 flow rate of 1,500 to 5,000 sccm; a N2 flow rate of 4,000 to 30,000 sccm; a SiH4/NH3 ratio of 0.2 to 0.04, a temperature of 350° C. to 550° C., a pressure of 2 to 10 Torr; a high frequency power of 40 to 300 watts and a low frequency power of 0 to 10 watts.
In other embodiments of the present invention, a dielectric layer exhibiting high tensile stress may be formed by depositing the dielectric layer by chemical vapor deposition and then treating the deposited dielectric layer with ultraviolet or electron beam radiation to increase its tensile stress.
In accordance with embodiments of the present invention, the stressed layer is applied at a relatively low temperature. Accordingly, the present invention enables deposition of a tensile or compressive stressed layer in transistors having nickel silicide layers formed on source/drain regions and gate electrodes, without exceeding the thermal stability limits of the nickel silicon layers. The present invention is also applicable to transistors comprising other metal silicides, such as cobalt silicide. In cobalt silicidation, a separate layer of silicon is deposited prior to depositing a layer of cobalt and implementing silicidation.
An embodiment of the present invention is schematically illustrated in
Another embodiment of the present invention is schematically illustrated in
Silicon nitride spacers 35 are then formed on silicon oxide liner 34 as by employing PECVD followed by etching. Subsequently, silicidation is implemented, as by forming a layer of nickel silicide 40 on the upper surface of gate electrode 32, as illustrated in
As illustrated in
Another embodiment of the present invention is schematically illustrated in
As illustrated in
Subsequently, a mask 110, e.g., photoresist or hard mask is applied over the PMOS transistor, as illustrated in
The present invention provides methodology enabling the fabrication of high quality, high operating speed, micro-miniaturized semiconductor devices based upon strained lattice technology, with maximized transistor drive currents. The inventive methodology can be practiced utilizing conventional processing techniques and instrumentalities at rates consistent with the throughput requirements of automated fabrication techniques, and is fully compatible with conventional process flow for the manufacture of high-density integrated semiconductor devices.
The present invention enjoys industrial applicability in fabricating various types of semiconductor devices. The present invention enjoys particular industrial applicability in fabricating micro-miniaturized semiconductor devices with high operating speeds.
In the previous description, numerous specific details are set forth, such as specific materials, structures, reactants, processes, etc., in order to provide a better understanding of the present invention. However, the present invention can be practiced without resorting to the details specifically set forth. In other instances, well-known processing materials and techniques have not been described in detail in order not to unnecessarily obscure the present invention.
Only the preferred embodiment of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is susceptible of changes or modifications within the scope of the inventive concept as expressed herein.
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|U.S. Classification||257/19, 257/E21.635, 257/18, 257/E29.056, 257/E21.633|
|International Classification||H01L21/336, H01L21/8238, H01L29/10, H01L31/072|
|Cooperative Classification||H01L29/6653, H01L29/665, H01L29/7843, H01L29/6656, H01L29/1054, H01L21/823828, H01L21/823807|
|European Classification||H01L29/66M6T6F6, H01L29/66M6T6F10, H01L29/78R2, H01L29/10D2B4, H01L21/8238G, H01L21/8238C|
|May 5, 2004||AS||Assignment|
Owner name: ADVANCED MICRO DEVICES, INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SUN, SEY-PING;BROWN, DAVID E.;REEL/FRAME:015299/0667
Effective date: 20040414
|Oct 31, 2006||CC||Certificate of correction|
|Dec 19, 2006||CC||Certificate of correction|
|Oct 23, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Oct 30, 2013||FPAY||Fee payment|
Year of fee payment: 8